Many factors are involved in the pathogenesis of hypertensive cardiovascular disease. A relatively few cases are due to overproduction of the mineralocorticoid aldosterone or of certain glucocorticoids. A number of clinical features of the disease have also led investigators to implicate the steroids as contributing to the elevated blood pressure in a substantial proportion of other cases as well. However, evidence accumulated to date on this question has been conflicting. The present proposal calls for approaching this problem in a different way. We shall develop an assay for mineralocorticoid activity which does not depend on measuring a particular steroid, but instead reflects the composite mineralocorticoid activity of a sample. The assay is a receptor competition technique utilizing renal mineralocorticoid receptors which generally bind mineralocorticoids proportionally to steriods' mineralocorticoid activity. A sample's mineralocorticoid activity would thus be related to its ability to inhibit binding of radioactive aldosterone to the receptors. Samples with excess activity, regardless of the nature of the steroid or whether the excess is due to a combination of steroids, should show increased inhibition. We would like to measure in this way the mineralocorticoid activity of samples from patients with various types of hypertension. Such data will provide information as to the extent to which mineralocorticoids are elevated in "essential" hypertension which is clearly a major risk factor in coronary artery disease, stroke and heart failure.